Research reveals fault geometry that forms Himalayas
Researchers have shed new light on the fault responsible for a 2015 earthquake that killed 9,000 people – information that will allow officials to better prepare for future shakers.
A new understanding of a fault that caused a deadly magnitude 7.8 earthquake can help scientists better understand where and when the next big one will hit.
For decades, scientists have debated the structure of the Main Himalayan Thrust – the fault responsible for a 2015 earthquake that killed nearly 9,000 people, injured 22,000 and destroyed 600,000 homes in Gorkha, Nepal. This fault is a direct result of ongoing collision between two tectonic plates – the Indian and Eurasian – that gives rise to the Himalayas.
A collaboration of Stanford, Oregon State, UT El Paso and UC Riverside with the Government of Nepal’s Department of Mining and Geology has determined a new geometric model for the fault that will allow officials to better prepare for future shakers. The team’s work is detailed in a paper published Nov. 11 in Nature Geoscience.
“Our images provide a new view in high-resolution of the way multiple earthquake faults build the Himalaya, stacking slices of rock from south to north,” said co-author Simon Klemperer, a geophysics professor in the School of Earth, Energy & Environmental Sciences (Stanford Earth). “They give us clues to which faults broke and why.”
Klemperer’s previous work on the Gorkha earthquake involved investigation of the entire aerial extent of the main fault, he said. The new images are from an analysis of the distribution and orientation of aftershocks of the quake.
Immediately following the earthquake, Klemperer and his collaborators received emergency funding from the U.S. National Science Foundation to rush to Nepal the dozen seismometers that Stanford owns to become part of a network of 45 seismometers in the ground. The deployment was complicated by the difficulty of traveling in high-altitude regions with poor infrastructure damaged further by ongoing earthquake and monsoon-induced landslides.
Speed was essential because the rate of occurrence of aftershocks rapidly decreases after the main earthquake, and the existing network of aftershock-measuring devices, known as seismic stations, was very limited. Without data on the aftershocks, including their locations and magnitudes, it would not have been possible to develop this more detailed understanding of the fault, according to Klemperer.
The Stanford seismometers were kept in place for one year after the main Gorkha earthquake, and were visited twice in that period to download data and service the instruments. The detailed locations of over 8,000 small earthquakes recorded by the temporary array of devices allowed researchers to recognize that what had previously been thought of as a single earthquake fault actually consists of multiple earthquake faults.
“We learned that in a crucial segment of the Main Himalayan Thrust east of Kathmandu, two fault planes overlap by 20 kilometers, connected by multiple steeper faults,” Klemperer said. “This so-called “duplex” structure shows how shortening – the convergence between the Indian and Asian tectonic plates – is taking place.”
Now the researchers want to find out whether the same duplex structure that controlled the location and rupture of the April 2015 magnitude 7.8 earthquake is present along the entire 1,000-kilometer length of the Main Himalayan Thrust from Pakistan to Myanmar.
This story was adapted from a press release issued by UC Riverside.